Magnetic recording media, magnetic recording media fabrication method, and fabrication equipment

ABSTRACT

A magnetic recording medium fabrication device includes a cooling drum around which a substrate runs while being cooled thereby, an ion gun arranged upstream to a vapor deposition station for kicking out particles absorbed on the plane of the substrate, a cooling body arranged between the cooling drum and ion gun for absorbing kicked out particles and a vapor deposition device for depositing a magnetic layer on the substrate at the vapor deposition station. The magnetic particles forming the magnetic layer that have residual magnetization vectors within +/-10 DEG  of the easy axis direction including the magnetic anisotropy of the medium are greater than or equal to 70% and less than or equal to 90% of the total amount of magnetic particles.

This application is a Divisional of parent application Ser. No.08/395,818, filed Feb. 28, 1995 now U.S. Pat. No. 5,569,523.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to thin-film magnetic recording media ofexcellent high-density recording characteristics, a method for theirmanufacture, and the fabrication equipment thereof.

2. Description of the Prior Art

Magnetic recording and playback systems with increasingly high-densityrecording characteristics have come into being. This has created anincreasing demand for magnetic recording media with superior short-waveread/write characteristics. The majority of the magnetic recording mediacurrently in use are coated magnetic recording media which are made byapplying a coating of magnetic powder to a substrate. Althoughimprovements have been made to satisfy the demand, efforts to achievecontinued improvements have encountered certain limits.

To overcome the limits, thin-film magnetic recording media have beendeveloped. These recording media, which are produced by the vacuum vapordeposition method, the sputtering method, or the plating method, offerexcellent short-wave read/write characteristics. For thin-film magneticrecording media, the use of the following magnetic layers is beingconsidered: Co, Co--Ni, Co--Ni--P, Co--O, Co--Ni--O, Co--Fe--O,Co--Ni--Fe--O, Co--Cr, and Co--Ni--Cr.

From the point of view of the suitability of application to magnetictape, Co--O and Co--Ni--O films, which are partially oxidized films, areconsidered to be the best. A vapor deposition tape in which Co--Ni--O isused as a magnetic layer has already been commercialized as a Hi8 VCRtape (ME tape). From a production efficiency standpoint, the vacuumvapor deposition method with oblique incidence is used as a method forproducing thin-film magnetic recording media.

A detailed explanation of one example of a vapor deposition tapefabrication method follows, with reference to FIG. 12. FIG. 12 shows anexample of the internal configuration of the continuous vacuum vapordeposition apparatus for producing vapor deposition tapes by obliqueincidence.

Substrate 100, composed of a polymer material, runs in the direction ofarrow R along a cylindrical drum 200. Reference numerals 201 and 202,respectively, denote a supply roll and a takeup roll for substrate 100.Reference numeral 203 denotes a free roller, several of which areprovided at appropriate locations to ensure that substrate 100 runsevenly. In some cases cylindrical drum 200 is cooled by some coolingmedia, such as cooling water, in order to prevent thermal damage to thesubstrate from radiation heat from the evaporation source during thevapor deposition process or from the heat of condensation that occurswhen evaporated atoms deposit on the substrate.

The deposition of evaporated atoms, vaporized from evaporation source120, onto substrate 100 forms a magnetic layer. An electron beamevaporation source is well suited to be evaporation source 120. In thissource, an alloy based on cobalt is filled as evaporation substance 130.The reason for the use of an electron beam evaporation source as anevaporation source is to vaporize high-melting-point metals, such ascobalt, at a high rate of evaporation. In the figure, electron beam 110is depicted schematically in terms of an arrow.

Reference numerals 150 and 151 denote shielding plates that are providedin order to prevent the deposition of superfluous evaporated atoms ontothe substrate and to define the range in which evaporated atoms strikesubstrate 100. A magnetic layer is formed when the evaporated atoms,passing through opening 180 composed of the shielding plate, reach thesubstrate. The incident angle of evaporated atoms is defined as theangle formed by an incident direction of evaporated atoms and a linenormal to substrate 100. Shielding plate 151 defines the initialincident angle φi. Likewise, shielding plate 150 defines the finalincident angle φf. It should be noted that the initial incident angle φiin the fabrication of Hi8 VCR tape ME is approximately 90°, and thefinal incident angle φf is approximately 30°. φi is 90° when evaporatedatoms are in contact with substrate 100, in which case shielding plate151 can be omitted.

An oxygen supply nozzle 170 is provided at the edge of shielding plate150 in order to introduce oxygen into the vacuum tank during vapordeposition. By optimizing the amount of oxygen introduced, vapordeposition tapes of excellent read/write characteristics and practicalutility can be obtained.

The magnetic layer of the magnetic recording medium thus fabricated hasa columnar structure, and its easy axis is inclined relative to the linenormal to the magnetic layer. In other words, the easy axis is neitherin the film nor in the direction of the line normal to the film surface.Rather, it is in a direction that is slanted with respect to the normalline on the normal surface, which includes the incident direction ofevaporated atoms with respect to the substrate. For example, incommercial Hi8 VCR ME tapes, the easy axis is inclined approximately 20°on the normal surface that includes the lengthwise direction of thetape. Here, the lengthwise direction of a tape is the direction alongthe length of the tape. In the fabrication equipment shown in FIG. 12,this direction is the direction in which substrate 100 runs. Themagnetization that is recorded by a ring-type magnetic head remains inthe direction of the obliquely slanted easy axis and forms amagnetization mode different from conventional longitudinal recording.

The formation of such a slanted magnetization mode produces asignificant improvement in high-density recording characteristics overconventional longitudinal recording media.

Further, to improve the read/write characteristics and practicalutilization characteristics, a double-layer structure magnetic layer hasbeen proposed (Japanese Patent laid-Open Publication H3-54719). As notedabove, when a magnetic layer is formed by the oblique vapor depositionmethod relative to a running substrate, the incident angle varies froman initial incident angle to a final incident angle between the spotwhere the film formation process is begun and the spot where the filmformation process is terminated. As a result, the columnar crystalparticles that compose the film are inclined and bend relative to thesubstrate surface. In a double-structure magnetic layer, the performancecharacteristics of the magnetic layer can be varied according to theangle of inclination of the columnar crystal particles that compose themagnetic layers.

For example, if the angle of inclination of the columnar crystalparticles for a layer is opposite to the direction in which thesubstrate runs, during read/write, the change in playback output due toa relative moving direction between the ring-type magnetic head and themagnetic layer tends to decrease. Further, it has been proposed to makethe film thickness of the lower magnetic layer greater than that of thetop magnetic layer in order to reduce the change in playback output(Japanese Patent laid-Open Publication H3-178028).

If the direction of inclination of the columnar crystal particles in thedifferent layers is the same as the running direction of the substrate,the change, during read/write, in playback output due to a relativemoving direction between the ring-type magnetic head and the magneticlayer tends to increase. However, in a certain direction, high playbackoutput can be obtained. Further, a proposal has been made to make theoxygen content of the top magnetic layer greater than that of the bottommagnetic layer in order to achieve a better head touch and to improvethe tape's durability (Japanese Patent laid-Open PublicationS62-236122). Both approaches offer the advantage of decreasing the noiselevel, as compared to a single-layer magnetic layer, by effecting adouble-layer structure.

In both the single- and double-layer structures, the film thickness ofthe magnetic layer is approximately 0.2 μm.

SUMMARY OF THE INVENTION

An essential object of the present invention is to offer magneticrecording media of excellent high-density recording characteristics, afabrication method thereof, and fabrication equipment.

The first fact of the present invention, relating to magnetic recordingmedia, is characterized in the use, in the normal surface that includesthe direction of tape run, of a ferromagnetic thin-film magnetic layerin which 70% to 90% of the total amount of magnetic particles have aresidual magnetization vector within ±10° of the easy axis directionthat includes the shape magnetic anisotropy of the medium.

By suppressing the dispersion of the easy axes of magnetic particles,the dispersion of magnetic flux near the magnetic layer surface can becurbed. The resulting stabilization of the magnetization vector, due tothe high magnetic anisotropy in an optimized easy axis direction,produces high playback output and low noise. If a ring-type magnetichead is used as a magnetic head, and to ensure the effective action ofthe magnetic flux from the magnetic layer on the magnetic head, the easyaxis direction, including the shape magnetic anisotropy of the medium,must be inclined 65° to 80° preferably 70° to 75°, from the directionnormal to the film surface.

The fabrication equipment for the magnetic recording medium of thepresent invention is a vapor deposition system for producing themagnetic layer for the aforementioned magnetic recording media. Theconstituent element of this system is characterized in that a coolingdrum is provided in a vacuum tank in order to allow the substrate to runalong the drum, an ion gun is provided at an upstream position of theaforementioned substrate run to a shielding plate that is provided inorder to define an initial incident angle of evaporated atoms relativeto the substrate, and, further, a cooling body is provided between theion gun and the cooling drum.

The fabrication method for the magnetic recording medium of the presentinvention is designed to produce the magnetic layer for the magneticrecording media using the fabrication equipment for the magneticrecording media. The constituent element of this fabrication method ischaracterized in that ions from the ion gun are allowed to strike thesubstrate surface at a maximum acceleration voltage of 400 V, and athin-film magnetic layer is formed by holding the temperature of thecooling body below that of the cooling drum.

In the above fabrication equipment and fabrication method, the substratesurface is irradiated with low-energy ions having a maximum accelerationvoltage of 400 V. This removes any gas that was physically adsorbed onthe substrate surface and forms a thin-film by keeping the substrateclean even when a cooling drum is used. This substantially suppressesany dispersion of the easy axes of the magnetic particles due to adecrease in substrate temperature.

The second magnetic recording medium of the present invention is athin-film magnetic recording medium composed of a magnetic layer whosemain constituents are cobalt and oxygen. The constituent element of thismagnetic recording medium is characterized in that the film thickness ofthe magnetic layer is greater than or equal to 0.05 μm and less than orequal to 0.12 μm; the magnetic layer is composed of a first magneticlayer that is formed on the substrate and a second magnetic layer thatis formed on the first magnetic layer; the columnar particles that formthe first and second magnetic layers are inclined in a substantiallysame direction; and that the film thickness of the second magnetic layeris greater than or equal to 50%, and less than or equal to 80%, of thetotal film thickness of the magnetic layers.

In the above constituent element, the minimum film thickness of amagnetic layer can be derived from the tolerance range for playbackoutput; similarly the maximum film thickness of a magnetic layer can bederived from the noise tolerance range. The first layer of the magneticlayers principally has a shape magnetic anisotropy and serves as anunder layer. Therefore, it is not necessary that this layer has a largefilm thickness. On the other hand, the second of the magnetic layers isthe principal magnetic layer. It has a large magnetocrystallineanisotropy due to the effects of the first magnetic layer, which is anunder layer, and due to the particular fabrication method employed, aswill be detailed later. In the second magnetic layer, which is theprincipal magnetic layer, the greater the film thickness is, the betteris the read/write characteristics in this short-wave region. To ensurefavorable read/write characteristics, the layer film thickness of themagnetic layer should be greater than or equal to 0.06 μm and less thanor equal to 0.1 μm, and the film thickness of the second magnetic layershould be greater than or equal to 60% and less than or equal to 75% ofthe total film thickness of the magnetic layers.

The method for the fabrication of the second magnetic recording mediumof the present invention involves vapor deposition on a substrate thatruns along the contact surface of a cylindrical drum. It is a method forthe fabrication of the aforementioned second magnetic recording medium.The constituent element of this method is characterized in that, duringa sequential formation of first and second magnetic layers and if anangle formed by a line normal to the substrate and an incident directionof evaporated atoms is defined as the incident angle, the incident angleat the beginning stage of the formation of the aforementioned first andsecond magnetic layers is greater than the incident angle at the end ofthe formation process, the incident angle at the end of the formation ofthe first magnetic layer is greater than the incident angle at the endof the formation of the second magnetic layer, and the ratio of (amountof introduced oxygen)/(rate of film deposition) during the formation ofthe first magnetic layer is greater than the ratio of (amount ofintroduced oxygen)/(rate of film deposition) during the formation of thesecond magnetic layer.

A large incident angle and a large ratio of (amount of introducedoxygen)/(rate of film deposition) ensure that the resultant firstmagnetic layer is a film that has a large shape magnetic anisotropy andexcellent under layer properties. The second magnetic layer, formed onthe first magnetic layer, is a film endowed with a largemagnetocrystalline anisotropy.

The fabrication equipment for the second magnetic recording medium ofthe present invention is designed to achieve high production efficiencyfor the fabrication of the second magnetic recording medium according tothe aforementioned fabrication method for the second magnetic recordingmedium. Its constituent element is characterized in that first andsecond evaporation sources are provided along the substrate runningdirection on a cylindrical drum, such that these sources are located onthe upstream side of the substrate running direction relative to theperpendicular straight line that passes through the center of thecylindrical drum; a shielding plate having both first and secondopenings corresponding to the respective evaporation sources is placedbetween the first and second evaporation sources on the one hand and thecylindrical drum on the other; the distance between the perpendicularstraight line passing through the center of the cylindrical drum and thecenter of the evaporation unit of the first evaporation source isgreater than the radius of the cylindrical drum; the distance betweenthe perpendicular straight line passing through the center of thecylindrical drum and the center of the evaporation unit of the secondevaporation source is less than the radius of the cylindrical drum; andthat the first evaporation source is located at a position higher thanthe horizontal position of the second opening.

Because this method is capable of forming a double-layer structuremagnetic layer in a single substrate run, it can achieve a highproductivity. Because the first magnetic recording medium need not bethick, only a small first evaporation source is used. Further, thepositioning of the first evaporation source so that it does not impedegas evacuation from the second opening ensures the production ofhigh-performance magnetic layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given below and the accompanying drawings wherein:

FIG. 1 is a cross-sectional view showing a schematic internal structureof the vapor deposition equipment which is used in the fabricationmethod for the first magnetic recording medium of the present invention;

FIG. 2 is a perspective view showing the positional relationship betweenthe ion gun and the cooling body in the fabrication equipment for thefirst magnetic recording medium of the present invention;

FIG. 3 is a cross-sectional view of a cooling drum shown in FIG. 1;

FIG. 4 is a cross-sectional view along line IV--IV of FIG. 3;

FIG. 5 is a cross-sectional view showing a schematic view of the firstmagnetic recording medium in an embodiment of the present invention;

FIG. 6A shows the distribution of residual magnetization vectors thatresult when a magnetic field is applied along the length of a tape;

FIG. 6B shows the distribution of residual magnetization vectors thatresult when a magnetic field is applied at an angle θ from the directionalong the length of a tape;

FIG. 7 is a cross-sectional view showing a schematic view of thestructure of the second magnetic recording medium of the presentinvention;

FIG. 8 is a cross-sectional view showing a schematic view of theinternal structure of the fabrication equipment for the second magneticrecording medium of the present invention.

FIG. 9 shows the playback output and noise as a function of the filmthickness of the first magnetic layer;

FIG. 10 shows the playback output and noise as a function of the filmthickness of the second magnetic layer;

FIG. 11 shows the playback output and noise as a function of the amountof oxygen introduced during the formation of the second magnetic layer;

FIG. 12 is a cross-sectional view showing a schematic view of theinternal structure of the conventional magnetic recording mediumfabrication equipment.

DESCRIPTION OF PREFERRED EMBODIMENTS

A detailed description of the present invention is given below withreference to the drawings.

FIG. 1 is a cross-sectional view showing a schematic internal structureof the vapor deposition equipment which is used in the fabricationmethod for the first magnetic recording medium of the present invention.

As shown in FIG. 1, a vacuum tank 50 is divided into a subchamber 51 ofa relatively small volume and a main chamber 52 of a relatively largevolume with two partition wall 53 and 54 forming an aperturetherebetween. These chambers 51 and 52 are evacuated by vacuum pumps 55and 56, respectively.

In subchamber 51, a supply roll 201 for supplying a film substrate 100,made of a polymer material and a takeup roll 202 for winding up amagnetic tape having a magnetic layer formed on the substrate 100.

In main chamber 52, a cylindrical drum 200 is rotatably housed and, uponforming the magnetic layer, is rotated around the center axis thereof ina direction of arrow R at a constant speed by a suitable drivingmechanism (not shown). A beam guide 61 is formed on a sidewall of tank50 on the side of main chamber 52 which extends upwardly and obliquelyand an electron gun 62 is mounted on the upper end of beam guide 61.Electron gun 62 generates an electron beam 110 directed to anevaporation source 120 arranged at the bottom side of main chamber 52.

In FIG. 1, substrate 100 composed of a polymer material runs in thedirection of arrow R along the contact surface of cylindrical drum 200.A thin-film is formed by the deposition of evaporated atoms on substrate100. Reference numeral 170 denotes an oxygen supply nozzle. Shieldingplates 150 and 151 define the incident angle of evaporated atoms.Cylindrical drum 200 uses a cooling drum that performs cooling by meansof a cooling medium, as will be explained later. These components ofFIG. 1 are largely similar to those in FIG. 12 depicting conventionalequipment. The difference between fabrication equipment for the firstmagnetic recording medium of the present invention and conventionalequipment lies in ion gun 105 and cooling body 106 that are providedabove shielding plate 151 on the upstream side of the path along whichthe substrate runs.

The following is an explanation of ion gun 105 and cooling body 106.

FIG. 2 is an enlarged perspective view for showing the positionalrelationship between shielding plate 151, ion gun 105 and cooling body106. Ion gun 105 is similar to that which is used in ion-beamsputtering, ion milling, or in the pretreatment of substrates. Grid 108of ion gun 105 emits accelerated ions 109, such as argon, nitrogen,hydrogen, and oxygen. Typically Argon is used. To prevent ions 109 fromstriking cooling body 106, a shielding plate 107 is provided between iongun 105 and cooling body 106. When cylindrical drum 200 is cooled, theout-gas, whose main constituent is water, which is produced from thevarious components of the equipment during vapor deposition, tends to beadsorbed avidly by substrate 100. Therefore, the adsorbed gas is knockedoff by the impact of ions 109 from ion gun 105 before a thin-film isformed on substrate 100. An excessively high ionic energy during thisprocess degrades substrate 100. Although not stated in the body of thistext, an electron gun is used in some cases to affix substrate 100 ontocylindrical drum 200 to prevent the heat degradation of substrate 100.An excessively high ionic energy of ions 109 produced by ion gun 105during this process neutralizes electrons emitted by the electron gun,thus diminishing the electron gun's ability to affix the substrate. Themain purpose of ion gun 105 here is not to improve the surface qualityof substrate 100, but to remove the gas that was physically adsorbed onthe substrate surface. Therefore, it is not necessary that the ions beaccelerated to a high energy. For these reasons, the accelerationvoltage of ions should be less than or equal to 400 V. The gas that wasknocked off is adsorbed onto cooling body 106 that is cooled to atemperature less than the temperature of cylindrical drum 200, thuspreventing any re-adsorption of the gas onto substrate 100. Cooling body106 can be cooled by any method. A method that is favored because ofconvenience is to construct cooling body 106 as a pipe-shaped objectthrough which a cooling medium is allowed to circulate, as indicated inFIG. 2. To increase the surface area, the pipe-shaped object can beprovided with grills and plates. Such a feature is also desirable fromthe standpoint of increasing the efficiency with which the gas isadsorbed. Further, in some cases ion gun 105 is provided with aneutralizer (not shown in the figure), in addition to grid 108 foraccelerating ions. The neutralizer is a wire, composed of tungsten andother substances, through which a current is passed in order to generatehot electrons. The electrons neutralize the positive charge buildup thatis produced by the ionic bombardment.

Thus, even when a cooling drum is used, a thin-film can be formed in acondition in which substrate 100 is maintained in a clean state. In thismanner, the present invention can effectively implement the suppressionof the dispersion in the easy axes of magnetic particles that wouldotherwise occur when the substrate temperature is reduced.

As shown in FIG. 3, cooling drum 200 is formed as a double cylindercomprising an outer shell 300 and an inner shell 301. Space betweenouter shell 300 and inner shell 301 is radially partitioned by aplurality of partition walls 311 as shown in FIG. 4.

Axial parts of end plates 302 and 303 are rotatably supported by bearingmeans 304 and 305, respectively. Coolant is supplied from an innercentral conduit 312 and distributed to each partitioned conduit betweenouter shell 300 and inner shell 301 through each radial inlet tube 307.Coolant supplied at one end of each partitioned conduit 306 flows in anaxial direction of the drum 200 and is collected through each radialoutlet tube 308 to an outer central conduit 309. Then, coolant collectedis discharged through a rotary joint 310 to recycle it.

As indicated in FIG. 4, flow directions of adjacent partitioned conduits306 are set opposite to each other.

By this coolant circulation system, the surface of cooling drum 200 isheld at a homogeneous constant temperature.

FIG. 5 is a cross-sectional view showing a schematic view of the firstmagnetic recording medium in an embodiment of the present invention. Themagnetic recording medium shown in this figure comprises substrate 100and a magnetic layer 101 that is provided on the substrate. Althoughmagnetic layer 101 is depicted as a single layer in this embodiment, itcan also be a multi-layer structure.

Substrate 100 is made of a polyethylene terephthalate film, a polyimidefilm, a polyamide film, a polyether film, a polyethylene naphthalatefilm, and other polymer films, or a polymer film that contains an underlayer.

The following explains the formation of a Co--O thin-film as a magneticlayer in use of the conventional vacuum vapor deposition equipment shownin FIG. 12.

A magnetic layer of Co--O was formed, and a thin-film magnetic recordingtape was produced continuously on substrate 100 by vaporizing cobaltfrom evaporation material 130 that was heated by an electron gun and byintroducing oxygen gas into a vacuum chamber from oxygen supply nozzle170. In this embodiment, a polyethylene terephthalate film was used assubstrate 100. The running speed of this film was regulated so as toproduce a magnetic layer film thickness of 80 nm. Vapor deposition wasconducted by introducing oxygen from oxygen supply nozzle 170 at a rateof 1 liter per minute with an internal pressure inside the equipment of6.7×10⁻³ Pa. The temperature of cylindrical drum 200 supportingsubstrate 100 was maintained at 40° C. The initial incident angle φiused during the vapor deposition was 80° in all cases, whereas the finalincident angle φf was allowed to vary. Table 1 shows the conditionsunder which the magnetic layer was formed.

                  TABLE 1                                                         ______________________________________                                        Sample   φ.sub.i  φ.sub.f                                                                          Drum temp.                                       ______________________________________                                        1-1      80°   70°                                                                           40° C.                                    1-2      80°   65°                                                                           40° C.                                    1-3      80°   60°                                                                           40° C.                                    1-4      80°   55°                                                                           40° C.                                    1-5      80°   50°                                                                           40° C.                                    ______________________________________                                    

The following explains the formation of a Co--O thin-film as a magneticlayer in use of the magnetic recording medium fabrication equipment ofthe present invention shown in FIG. 1.

A magnetic layer of Co--O was formed, and a thin-film magnetic recordingtape was produced continuously on substrate 100 by vaporizing cobaltfrom evaporation material 130 that was heated by an electron gun and byintroducing oxygen gas into a vacuum chamber from-oxygen supply nozzle170. In this embodiment, a polyethylene terephthalate film was used assubstrate 100. The running speed of this film was regulated so as toproduce a magnetic layer film thickness of 80 nm. The initial incidentangle φi used during the vapor deposition was 80°, whereas the finalincident angle φf was 60°. Both cylindrical drum 200 and cooling body106 were cooled using a cooling medium, and their temperatures wereregulated. The amount of oxygen required decreased as cylindrical drum200 was cooled. When the drum temperature was -20° C., the amount ofoxygen introduced was 0.6 liter per minute and the pressure inside theequipment was 5.0×10⁻³ Pa. Argon was introduced into ion gun 105 at aflow rate of 10 cc/min. Although the ionic current density used in thisembodiment was 20 mA/cm², the density can be regulated appropriatelyaccording to the running speed of substrate 100. Table 2 shows theconditions under which the magnetic layer was formed.

                  TABLE 2                                                         ______________________________________                                                              Drum   Cooling  Acceleration                            Sample                                                                              φ.sub.i                                                                           φ.sub.f                                                                           temp.  body temp.                                                                             voltage                                 ______________________________________                                        2-1   80°                                                                            60°                                                                             20° C.                                                                       --       --                                      2-2   80°                                                                            60°                                                                             0° C.                                                                        --       --                                      2-3   80°                                                                            60°                                                                            -20° C.                                                                       --       --                                      2-4   80°                                                                            60°                                                                            -20° C.                                                                       -100° C.                                                                        --                                      2-5   80°                                                                            60°                                                                            -20° C.                                                                       --       300 V                                   2-6   80°                                                                            60°                                                                            -20° C.                                                                       -100° C.                                                                        300 V                                   2-7   80°                                                                            60°                                                                            -20° C.                                                                       -100° C.                                                                        400 V                                   2-8   80°                                                                            60°                                                                            -20° C.                                                                       -100° C.                                                                        500 V                                   2-9   80°                                                                            60°                                                                            -20° C.                                                                        -50° C.                                                                        300 V                                    2-10 80°                                                                            60°                                                                             0° C.                                                                         -50° C.                                                                        300 V                                   ______________________________________                                    

The distribution of residual magnetization vectors, the magneticanisotropy, and the read/write characteristics of the magnetic layerthus produced were evaluated.

The following is an explanation of the residual magnetization vectordistribution measurement method that was used to determinequantitatively the dispersion of the easy axes of the magnetic layer.

Normally, magnetization vectors are oriented in the direction of easyaxes. In the case of a thin-film, a magnetic anisotropy exists in planeof the film that tends to force the magnetization vectors to orientthemselves toward the in-plane of the thin-film. The easy axis that isdetermined solely by the magnetic anisotropy in the plane, naturally,occurs in the plane. The origin of the in-plane magnetic anisotropy is ashape magnetic anisotropy that originates from a macro shape that is athin-film. On the other hand, a magnetic anisotropy also exists thatoriginates from the magnetic anisotropy of the magnetic particles thatcomprise the thin-film. The easy axis, i.e., intrinsic easy axis,behaves as a function of the shape of the magnetic particles, theirorientation, their alignment, the crystallinity of the particles, andthe crystalline orientation of the thin-film as an aggregate of theparticles. If the direction of the latter magnetic anisotropy liesbetween the in-plane direction and the direction of the line normal tothe film, i.e., if an oblique magnetic anisotropy exists, the easy axisincluding the shape anisotropy of the thin-film lies between thedirection of the intrinsic easy axis and the in-plane direction. Theeasy axis that includes the shape magnetic anisotropy of the thin-filmis called the apparent easy axis of the thin-film. The magnetizationvector in a thin-film is stabilized in the direction of the easy axisthat includes the thin-film shape magnetic anisotropy.

Therefore, for a quantitative determination of the dispersion of easyaxes, it suffices to determine the distribution of residualmagnetization vectors.

The distribution of residual magnetization vectors can easily bemeasured using a vibrating sample magnetometer according to thefollowing procedures:

First, a magnetic field H(0) is applied on the film, in the direction inwhich the substrate runs, in order to saturate the magnetic layer. Afterthat, the magnetic field is removed. FIG. 6A shows the resultingdistribution of residual magnetization vectors in the plane of the film,where the residual magnetization in the lengthwise direction of the tapeis denoted as Mr(0). Then, a magnetic field H(θ) is applied on the filmin a plane that is perpendicular to the width direction of the tape in adirection which is slightly shifted by an infinitesimally small angle θfrom the lengthwise direction of the tape. After that, the magneticfield is removed and residual magnetization Mr(θ) in the lengthwisedirection of the tape is measured. FIG. 6B shows the resultingdistribution of residual magnetization vectors. In this figure, themagnetization vector that occurred in item A in FIG. 6A has reversed toB in FIG. 6B after the magnetic field H(θ) is applied. It should benoted that, except for A, the residual magnetization vectors undergo nochanges. Therefore, the difference between Mr(0) and Mr(θ) is equal tothe difference between the lengthwise-direction component of themagnetization vector A and the lengthwise-direction component of themagnetization vector B. This relationship is indicated by Equation 1. InEquation 1, V denotes the volume of the magnetic particles that existsin A, and Ms denotes the saturation magnetization. From Equation 1,volume V of the magnetic particles existing in A can be determined.

By performing this measurement repeatedly, it is possible to determinethe volume of the magnetic particles that have magnetization vectors invarious directions and to determine the distribution of magnetizationvectors. From the resulting distribution curve, volume ratio f of themagnetic particles having magnetization vectors within ±10° of easy axisβ was determined. This value was used as a measure that indicates thedegree of orientation of the easy axes. Specifically, the greater thevolume ratio f, the higher is the degree of orientation of easy axes andthe smaller is their dispersion. Incidentally, measurements taken ofcommercial ME tape indicated a volume ratio f of 62%. ##EQU1##

In order to determine the magnetic anisotropy of the magnetic layer, thedirection β of the easy axis, including the shape magnetic anisotropy ofthe thin-film and magnetic anisotropy field H_(K) * in direction β, wereevaluated using a torque magnetometer according to the measurementmethod described in IEEE Trans. on Magn 27 (1991) pp. 4864-4866.

The read/write characteristics of the magnetic layer were measured usingan off-the-shelf 8-mm VCR unit. The playback output (C) and the noise(N) were evaluated at a 7 MHz recording frequency.

The results of these evaluations are shown in Tables 3 and 4. β is theangle between the easy axis and the film normal.

                  TABLE 3                                                         ______________________________________                                        Sample φ.sub.f                                                                          β  f    H.sub.K *                                                                              C     N                                   ______________________________________                                        1-1    70°                                                                           73°                                                                            85%  1180 kA/m                                                                              +3.7 dB                                                                             -1.3 dB                             1-2    65°                                                                           70°                                                                            80%  1125 kA/m                                                                              +3.2 dB                                                                             -1.1 dB                             1-3    60°                                                                           67°                                                                            73%  1040 kA/m                                                                              +2.2 dB                                                                             -0.8 dB                             1-4    55°                                                                           65°                                                                            71%  1010 kA/m                                                                              +1.9 dB                                                                             -0.6 dB                             1-5    50°                                                                           63°                                                                            65%   825 kA/m                                                                               0.0 dB                                                                              0.0 dB                             ______________________________________                                    

                                      TABLE 4                                     __________________________________________________________________________             Cooling                                                                             Accelera-                                                          Drum body  tion                                                           Sample                                                                            temp.                                                                              temp. voltage                                                                            f   H.sub.K *                                                                           C    N                                          __________________________________________________________________________    1-1  40° C.                                                                     --    --   85% 1180 kA/m                                                                            0.0 dB                                                                             0.0 dB                                    2-1  20° C.                                                                     --    --   75% 1065 kA/m                                                                           -1.2 dB                                                                            +0.4 dB                                    2-2  0° C.                                                                      --    --   77% 1080 kA/m                                                                           -0.9 dB                                                                            +0.3 dB                                    2-3 -20° C.                                                                     --    --   78% 1100 kA/m                                                                           -0.8 dB                                                                            +0.2 dB                                    2-4 -20° C.                                                                     -100° C.                                                                     --   79% 1115 kA/m                                                                           -0.7 dB                                                                            +0.2 dB                                    2-5 -20° C.                                                                     --    300 V                                                                              79% 1120 kA/m                                                                           -0.6 dB                                                                            +0.2 dB                                    2-6 -20° C.                                                                     -100° C.                                                                     300 V                                                                              88% 1190 kA/m                                                                           +0.5 dB                                                                            -0.2 dB                                    2-7 -20° C.                                                                     -100° C.                                                                     400 V                                                                              90% 1200 kA/m                                                                           +0.8 dB                                                                            -0.3 dB                                    2-8 -20° C.                                                                     -100° C.                                                                     500 V                                                                              --  --    --   --                                         2-9 -20° C.                                                                      -50° C.                                                                     300 V                                                                              83% 1155 kA/m                                                                           -0.2 dB                                                                             0.0 dB                                     2-10                                                                              0° C.                                                                       -50° C.                                                                     300 V                                                                              81% 1125 kA/m                                                                           -0.4 dB                                                                            +0.1 dB                                    __________________________________________________________________________

Table 3 indicates that as final incident angle φf becomes smaller,volume ratio f decreases, and magnetic anisotropy field H_(K) * alsodecreases. Specifically, there is a significant decrease in the propertywhen φf decreases from 55° to 50°. Apparently this phenomenon is causedby a rapid increase in film thickness due to the formation of film at alow incident angle. The read/write characteristic also declines as finalincident angle φf decreases in an apparent reflection of theaforementioned volume ratio and the value of the magnetic anisotropyfield. These results suggest that the desirable value of f is 70% orgreater, preferably 80% or greater. Similarly, the desirable value of βis 65° or greater, and that of H_(K) * is 1000 kA/m or greater. A filmfor which the value of β was greater than 80° was produced under filmformation conditions of an initial incident angle φi of 90° and a finalincident angle φf of greater than or equal to 80°. However, theresulting productivity was extremely low, and the resulting film wasextremely weak, and not suitable as a magnetic recording medium.Therefore, the desirable range of β is from 65° to 80°, inclusively.

The following is an description of the results shown in Table 4.

Samples 2-1, 2-2, and 2-3 were formed by varying the temperature of thecylindrical drum. The lower the temperature, the better were theread/write characteristics, apparently due to an increase in the shapemagnetic anisotropy due to the self-shadowing effect as the substratetemperature, i.e., the temperature of the cylindrical drum, decreasedduring film formation.

Samples 2-3, 2-4, 2-5, and 2-6 were produced in order to investigate theeffects of a cooling body as well as the effects of ion bombardment.When only a cooling body was used (2-4) or only ion bombardment wasconducted (2-5), only a few effects were observed compared to the sample(2-3) which was produced without the use of a cooling body and withoutreceiving any ion bombardment. The effect, however, was noticeable inthe sample (2-6) which received both. This effect is thought to be dueto the knocking off of the gas adsorbed on the substrate surface by ionbombardment and the efficient capture of the released gas by the coolingbody. Thus, the effect may reflect the fact that vapor depositionoccurred in a clean condition on the surface of the substrate which wasmaintained at a low temperature. It can be inferred that keeping thesubstrate surface clean enhances the crystallinity of the film, thusincreasing the contribution from the magnetocrystalline anisotropy, andthat reducing the substrate temperature simultaneously achieved anincrease in the shape magnetic anisotropy.

Samples 2-6, 2-7, and 2-8 were formed by varying the ionic accelerationvoltage during ion bombardment. The sample (2-7) produced by setting theacceleration voltage at 400 V exhibited the best read/writecharacteristics of the samples in this embodiment. The sample (2-8),produced by setting the acceleration voltage at 500 V, however,exhibited a degradation of, and damage to, the substrate because of toohigh an ionic energy. This hampered the evaluation of read/writecharacteristics. Therefore, for stable achievement of the effects of thepresent invention, the ion acceleration voltage should be set at 400 Vor less.

Samples 2-6 and 2-9 were produced by varying the temperature of thecooling body. Although both samples exhibited the effects of the presentinvention, the lower the temperature of the cooling body, the betterwere the results. The desirable temperature seems to be -100° C. orlower.

A comparison of samples 2-2 and 2-10 indicates that the effects of thepresent invention can be achieved even at a -50° C. cooling bodytemperature as long as ion bombardment is conducted.

There is a correlation between the volume ratio f of the samplesproduced under the aforementioned conditions, the magnetic anisotropyfield result Hk*, their values, and the read/write characteristics.Therefore, the incident angle was increased in order to obtain an fvalue greater than 90% or an Hk*, value greater than 1200 kA/m. However,the result produced an extremely decreased film strength, making theresulting film unsuitable as a magnetic recording medium.

Read/write characteristics, equal to, or even surpassing those shown inTable 3 and produced using a high incident angle, were achieved even ata low incident angle when ion bombardment was carried out by providingcooling bodies. This demonstrates that, by using the fabrication methodof the present invention, magnetic recording media with excellentread/write characteristics can be obtained at a high productionefficiency.

Although cobalt was used in this embodiment as a material forevaporation source 120, metals such as Fe and Ni, or alloys such asCo--Cr and Co--Ni, can also be used. This invention is also effective ina vapor deposition method in which no oxygen is introduced during vapordeposition.

The following is an explanation of the second magnetic recording medium,its fabrication method, and fabrication equipment.

FIG. 7 shows a schematic cross-sectional view of the magnetic layer ofthe second magnetic recording medium of the present invention. There isa first magnetic layer 102 on substrate 100. A second magnetic layer 103is on first magnetic layer 102. Thus, the magnetic layer of the magneticrecording medium comprises two stacked magnetic layers.

The principal components of the magnetic material are cobalt and oxygen.Cobalt is the best-suited thin-film magnetic layer because it is endowedwith a high saturation magnetization and a high magnetocrystallineanisotropy energy. The combination of cobalt and oxygen serves toenhance the properties of cobalt to the maximum extent.

To increase the energy of the magnetic layer due to the shape magneticanisotropy, the present invention employs a method consisting of twopoints: the first point involves the alignment of the direction ofinclination of the columnar particles in first magnetic layer 102 andsecond magnetic layer 103. The second point involves making the columnarparticles as straight as possible. As can be seen in the fabricationmethod which will be described later, a cylindrical drum is ill-suitedto making columnar particles straight. When a cylindrical drum is used,columnar particles curve. An important requirement is to make the curveas small as possible. The curvature should be less than 15°. Further,given that a ring-type magnetic head is used for read/write purposes,the inclination of columnar particles, in order to fully utilize theshape magnetic anisotropy of columnar particles, should be greater thanor equal to 20° and less than or equal to 35° from the substratesurface.

In order to increase the energy of the magnetic layer due tomagnetocrystalline anisotropy, in departure from the prior art (JapanesePatent laid-Open Publication H3-178028), the present invention uses aconfiguration in which first magnetic layer 102 is made thin and thesecond magnetic layer thick. Direct formation of a magnetic layer onsubstrate 100, as in this invention, often fails to produce a highcrystallinity. The reason for this condition appears to be that thevarious impurities, including gases, that occur in the neighborhood ofthe polymer surface inhibit crystalline growth. If the film is madethick, the crystallinity increases due to the preferred growthcharacteristic of crystals at the expense of an increased crystalgranularity and an increase in noise.

Therefore, in the present invention, first magnetic layer 102 isconsidered, crystallographically, to be the under layer for secondmagnetic layer 103, which is formed at the next step; and the two layersare stacked in such a way that the first magnetic layer is the thinnerof the two layers. However, although first magnetic layer 102contributes little as a magnetic layer from a magnetocrystallineanisotropy standpoint, because it possesses a shape magnetic anisotropy,it can naturally function as a magnetic layer. Since second magneticlayer 103 is formed on first magnetic layer 103, which is the underlayer, it can produce a relatively high crystallinity even at theinitial stages of film formation. Thus, second magnetic layer 103exhibits excellent magnetic layer properties, offering both a highmagnetocrystalline anisotropy and a high shape magnetic anisotropy. Ifthe magnetocrystalline anisotropy is strong, however, the direction ofits easy axis may not agree with the direction of columnar particles. Inthe present invention, the incident angle used and the amount of oxygenintroduced are adjusted within an allowable range during the formationof the two magnetic layers so that the two directions agree, i.e., themagnetic anisotropy energy of the magnetic layers increases. In view ofthe fact that a ring-type magnetic head may be used for read/write, theeasy axis direction of the magnetic layer should be adjusted so that itis greater than or equal to 65° and less than or equal to 80° from theline normal to the film. It should be noted that in the present context,the term "direction of easy axis" encompasses the shape magneticanisotropy of the thin-film. The so-called intrinsic easy axisdirection, from which the influence of the shape of the thin-film hasbeen eliminated, is a direction higher from the substrate surface thanthe easy axis direction in the present context. If the easy axisdirection of a magnetic layer is greater than 80° from the line normalto the film, an increase in noise results, apparently due to theformation of a zigzag magnetic wall due to the collision ofmagnetizations. Conversely, if the easy axis direction of a magneticlayer is less than 65° from the line normal to the film, a smallperpendicular component of the recording magnetic field in the ring-typemagnetic head reduces the recording efficiency, and produces reducedplayback output and an increased spacing loss factor.

An explanation of the thickness of a magnetic layer follows. For firstmagnetic layer 102 to be able to function as a under layer for secondmagnetic layer 103, its thickness must be at least 0.01 μm,approximately. A thickness greater than approximately 0.6 μm causes anincrease in granularity, as a result of the increased film thickness,and leads to an increased noise level. Therefore, the optimal filmthickness of first magnetic layer 102 is greater than or equal to 0.01μm and less than or equal to 0.6 μm. Further, the optimal range of thetotal thickness of the magnetic layer in which both first magnetic layer102 and second magnetic layer 103 are combined is between 0.5 μm and0.12 μm. A total magnetic layer thickness of less than or equal toapproximately 0.05 μm results in a precipitous decrease in the playbackoutput in the long-wave region as well as in the short-wave region withan attendant difficulty in tracking adjustment. On the other hand, atotal thickness greater than or equal to approximately 0.12 μm causes anincrease in noise with a reduced C/N ratio. The optimum thickness ratiobetween magnetic layers and the optimum total thickness varies with thetype of head used depending on the write performance of the head and thecoercive force of the magnetic layer. In the film thickness range forthe aforementioned magnetic layer of the present invention, the coerciveforce of the first magnetic layer tends to rise with an increase in filmthickness, whereas the coercive force of the second magnetic layer tendsto increase as the film thickness decreases. Therefore, in the case of aferrite ring head, in which the saturation magnetization is small andthe gap length is large, the total thickness of the magnetic layersshould be large and the film thickness ratio for the second magneticlayer should be increased in order to set the coercive force for theentire magnetic layer low. In the case of a metal ring head, in whichthe saturation magnetization is large and the gap length small the totalthickness of the magnetic layers should be small and the film thicknessratio for the second magnetic layer should be reduced in order to setthe coercive force for the entire magnetic layer high.

The following is a description of the method of fabrication of magneticrecording media of the present invention with reference to FIG. 12.Since FIG. 12 was already referred to in the description of aconventional example, a description of the elements of the figure isomitted.

As stated above, the method for the fabrication of magnetic layers, aswell as their constitution, has a large bearing on the production of ahigh magnetic anisotropy energy. In particular, the incident angle ofevaporated atoms with respect to the substrate and the amount of oxygenthat is introduced are especially important. The magnetic layer of thepresent invention can be obtained using the equipment of FIG. 12 bysetting various conditions and by repeatedly conducting vapordeposition. It should be noted, however, that after a first magneticlayer is formed, the takeup roll should be rewound once before a secondmagnetic layer can be formed.

An explanation of incident angles follows. An incident angle is definedas the angle formed by the line normal to the substrate and the incidentdirection of evaporated atoms.

For the formation of either a first magnetic layer or a second magneticlayer, the initial incident angle φi should be made larger than thefinal incident angle φf for two reasons. The first reason concerns themechanical strength of the film. A final incident angle φf that islarger than the initial incident angle φi results in a low density onthe film surface, i.e., the surface of the magnetic layer. A largeincident angle produces a large self-shadowing effect with an attendantdecrease in density. A low density translates into a reduced mechanicalstrength, and an inadequate mechanical strength leads to a greaterpropensity of the magnetic layer surface to become scratched, which isundesirable. The second reason concerns crystal growth. The c-axis,which is the easy axis direction for cobalt, normally growsperpendicularly with respect to the substrate, and crystal that growsubsequently have the property that they grow in such a way that theircrystalline axes are aligned. If the c-axis is to be inclined, theincident angle must be increased. However, an increase in the incidentangle increases the dispersion of the c-axis. And, even though theextent of dispersion is large, the slope of the c-axis thus formed isinherited by other c-axes even when the incident angle changessubsequently. Therefore, in order to cause an inclination in the easyaxis direction, the initial incident angle must be increased.

The incident angle for the first magnetic layer should be larger thanthat for the second magnetic layer. The final incident angle φf shouldbe made especially large. The reason is that, although the incidentangle is not important if the first magnetic layer is considered to bestrictly an under layer, the incident angle should be increased in orderto sufficiently induce the shape magnetic anisotropy, if it isconsidered to be a magnetic layer. Further, since the first magneticlayer is not exposed to the surface of the medium, it need not bemechanically strong. The initial incident angles φi for the two magneticlayers should be either equal or the initial incident angle for thefirst magnetic layer should be larger than that for the second magneticlayer. At any rate, however, these angles should be less than or equalto 85°, because at an initial incident angle larger than 85°, thedispersion of the c-axis increases greatly. The region for which theincident angle is greater than or equal to 85° is one in which the lociof evaporated atoms form a tangent to the contact surface of cylindricaldrum 200 if the evaporated atoms are assumed to advance in a straightline. It is also an area in which the attachment effect approaches 0percent. If, however, evaporated atoms advance while colliding with eachother or with a residual gas, the form in which evaporated atoms depositon the substrate is likely to be unstable. In the present invention, anincident angle greater than or equal to 85° is not used in order toproduce a high-performance magnetic layer with adequate control. Inorder to ensure that the slope of columnar particles is less than orequal to 35° from the substrate surface, the final incident angle φfmust be greater than or equal to 50°. Although the 50° final incidentangle may appear inadequate from the aforementioned results (Table 3),it is an appropriate range for a double-layer structure magnetic layerin which the thickness per layer is small.

The amount of oxygen introduced during magnetic layer formationdetermines the saturation magnetization for the magnetic layer, and itis an important factor for the formation of a magnetic layer. Generally,the greater the saturation magnetization, the higher is the playbackoutput. However, a high playback output by itself is not beneficial.Since the saturation magnetization is an important factor thatdetermines the easy axis direction for the magnetic layer, there is anoptimum saturation magnetization. The larger the saturationmagnetization, the more closely the easy axis direction approaches thein-plane direction of the magnetic layer. Because of this fact, toolarge a saturation magnetization leads to an increase in noise. On theother hand, a small saturation magnetization results in a smallanisotropy energy for the magnetic layer, which is undesirable. It isimportant that the range of slope of the columnar particles forming themagnetic layer be adjusted from 20° to 35° by means of incident anglesand the range of the easy axis direction be adjusted from 65° to 80°from the film normal line by adjusting the amount of oxygen introduced.It should be noted, however, that the optimum amount of oxygenintroduced varies with the equipment configuration, the size of theequipment, the residual gas pressure inside the equipment, and the gasevacuation capability of the equipment. Therefore, it is difficult torepresent the optimal amount of oxygen introduced uniquely in terms ofspecific numerical values. Therefore, the optimum amount of oxygenintroduced should be determined on a case-by-case basis according to thetype of equipment used.

For the fabrication of the second magnetic recording medium of thepresent invention, it is necessary that the ratio of (amount ofintroduced oxygen)/(rate of film deposition) during the formation of thefirst magnetic layer be greater than the ratio of (amount of introducedoxygen)/(rate of film deposition) during the formation of the secondmagnetic layer. In terms of saturation magnetization, the saturationmagnetization of the first magnetic layer must be smaller than that ofthe second magnetic layer. In this regard, the present invention differsfrom the prior example (Japanese Patent laid-Open PublicationS62-236122). The first magnetic layer functions as an under layer forthe second magnetic layer and also as a magnetic layer in its own right.Whether the first magnetic layer is considered to be an under layer or amagnetic layer, the amount of oxygen introduced is important. The largerthe amount of oxygen contained, the higher is the functionality of thefirst magnetic layer as an under layer. As noted above, the importanceof the first magnetic layer lies in the shape magnetic anisotropy ofcolumnar particles. Therefore, the amount of oxygen introduced isimportant when the first magnetic layer is viewed as a magnetic layerrather than an under layer. Therefore, the function of the firstmagnetic layer as a magnetic layer has priority over the function of thefirst magnetic layer as an under layer. The first magnetic layer shouldbe formed at a high incident angle, which produces a high degree of theself-shadowing effect. During the formation of this layer, oxygen mustbe introduced in order to promote the magnetic separation betweencolumnar particles. Therefore, the ratio of (amount of introducedoxygen)/(rate of film deposition) for the first magnetic layer should bemade larger than that for the second magnetic layer, with a consequentreduction in saturation magnetization. Oxygen, however, should not beintroduced to an extent that it renders the first magnetic layernonmagnetic. In the second magnetic layer, on the other hand, the shapemagnetic anisotropy of columnar particles as well as themagnetocrystalline anisotropy make large contributions. As a generalrule, introducing a gas lowers the crystallinity. Therefore, for theformation of the second magnetic layer, priority should be given tominimizing the extent of decline in crystallinity, and the amount ofoxygen introduced should be held to a minimum in order to ensure theminimum necessary magnetic separation of columnar particles. Thus, theratio of (amount of introduced oxygen)/(rate of film deposition) must bemade as small as possible. During actual formation of a magnetic layer,the absolute amount of oxygen that is introduced can be higher for theformation of the second magnetic layer than for the formation of thefirst magnetic layer depending on the power of the electron beam that isdirected at the evaporation source and the conditions such as the rangeof incident angles. In some cases the converse is true.

The following paragraphs explain the fabrication equipment for thesecond magnetic recording medium of the present invention with referenceto FIG. 8. The equipment shown in FIG. 8 is capable of producing thesecond magnetic recording medium of the present invention with a singlerun of the substrate, thus substantially improving productivity.

In FIG. 8, two evaporation sources, 221 and 222, are provided along therunning direction of substrate 100 on a cylindrical drum 200. Firstevaporation source 221 is for the first magnetic layer, and secondevaporation source 222, for the second magnetic layer. Shielding plates261 and 260, and 251 and 250, that provide first and second openings,281 and 282 corresponding to the respective evaporation sources, areplaced between the first and second evaporation sources, 221 and 222,and cylindrical drum 200. At first opening 281 for the first magneticlayer, shielding plate 261 defines the initial incident angle φi1 forthe first magnetic layer. Similarly, shielding plate 260 defines thefinal incident angle φf1 for the first magnetic layer. Likewise, atsecond opening 282 for the second magnetic layer, shielding plate 251defines the initial incident angle φi2 for the second magnetic layer.Similarly, shielding plate 250 defines the final incident angle φf2 forthe second magnetic layer. Further, the first and second evaporationsources, 221 and 222, are provided on the upstream side of the directionin which substrate 100 runs relative to the perpendicular straight linethat passes through the center of cylindrical drum 200, such that thedistance between the perpendicular straight line passing through thecenter of cylindrical drum 200 and the center of the evaporation unit offirst evaporation source 221 is greater than the radius of cylindricaldrum 200; the distance between the perpendicular straight line passingthrough the center of cylindrical drum 200 and the center of theevaporation unit of second evaporation source 222 is less than theradius of cylindrical drum 200; and first evaporation source 221 islocated at a position higher than the horizontal position of secondopening 282.

In a process that forms the two magnetic layers simultaneously using theabove equipment configuration of the present invention, all parameters,other than the running speed of substrate 100, can be controlledindependently. Another significant feature of the present invention isits ability to maintain a low pressure for the residual gas in theneighborhood of the vapor deposition unit, which is an importantconsideration in the vapor deposition method. If, for example, firstevaporation source 221 is lower than the horizontal position of secondopening 282, first evaporation source 221 blocks the evacuation ofresidual gas from the neighborhood of second opening 282. If anothershielding plate is installed in order to prevent the evaporated atomsfrom first evaporation source 221 from reaching the second opening, thisshielding plate, too, will block the evacuation of residual gas from theneighborhood of second opening 282.

Electron-beam heating using a Pierce electron gun is suited as anelectron beam source for mass production purposes. However, installing aplurality of such electron guns will necessitate an increase inequipment size, and the effect of the inert gas that is introduced forconverging the electron beams will be considerable, thus leading to anincrease in the pressure of the residual gas in the neighborhood of anopening. Therefore, for the purpose of reducing the pressure of residualgas and the size of the equipment, the desirable approach is to directthe electron beam from one electron beam source to two evaporationsources by magnetic field deflection. In this case, the amount ofelectron beam power that is applied to a evaporation source can beregulated by controlling the proportion in which the electron beam isdistributed into the two evaporation sources.

When two evaporation sources are heated using electron beams 211 and212, measures should be taken so that the electron beam directed to aevaporation source does not intersect the evaporated atom stream flowingfrom the other evaporation source to an opening. In FIG. 8, for example,if the first evaporation source were located at a position beyondelectron beam 212, and away from cylindrical drum 200, electron beam 212would intersect the evaporated atom stream flowing from firstevaporation source 221 to opening 281. Such an arrangement would resultin a decrease in productivity, would require extra shielding plates, andtherefore would be highly undesirable.

First evaporation source 221 should be smaller than second evaporationsource 222. By constructing a small first evaporation source 221 andletting it approach cylindrical drum 200, it is possible to directelectron beam 212 at second evaporation source 222 at a sharper angle,thus enhancing both productivity and ease of control. The crucial pointin this equipment configuration is the fact that the first magneticlayer is thin and the second magnetic layer thick, which is a structuralcharacteristic of the magnetic layers of the magnetic recording mediumof the present invention. Evaporation source 221 for the first magneticlayer is situated exterior to the lower part of cylindrical drum 200 andforms a structure which is incapable of furnishing the highest possiblevapor density to the film formation process. However, because thisevaporation source is located close to cylindrical drum 200, theresulting rate of film deposition is substantially high, well within therealm of practical use. Therefore, the evaporation source for the firstmagnetic layer can be smaller than that for the second magnetic layerand requires only a smaller power for the electron beam. Thus, despiteincorporating two evaporation sources, the equipment can be extremelycompact.

Each of the two evaporation sources is provided with a set of openings,and each opening is provided with an oxygen supply nozzle. Oxygen isintroduced from oxygen supply nozzle 271, which is provided for thefirst magnetic layer between shielding plate 260 and cylindrical drum200. Similarly, oxygen is introduced from oxygen supply nozzle 272,which is provided for in the second magnetic layer between shieldingplate 250 and cylindrical drum 200. It is important to suppress theinflow of the oxygen introduced from oxygen supply nozzle 271, which isprovided for the first magnetic layer, into second opening 282. To thisend, measures should be taken such as conferring a key shape on the edgeof shielding plate 260.

A description of the present invention with reference to specificembodiments follows.

A Co--O film was formed as a magnetic layer using the magnetic recordingmedium fabrication equipment shown in FIG. 12. A polyethyleneterephthalate film 7 μm thick was used as substrate 100. The cylindricaldrum used, reference numeral 200, had a 1.5 m diameter.

(Embodiment 1)

A first magnetic layer was formed with an incident angle range of 80° to60°. Cobalt was loaded on evaporation source 120 and melted using a 50kW electron beam. Oxygen was introduced from oxygen supply nozzle 170 ata rate of 0.9 liter per minute. A film with a thickness of 0.005 μm to0.2 μm was formed by varying the running speed of substrate 100. Afterthe first magnetic layer was formed, the roll that was taken up wasrewound once. On the first magnetic layer thus formed, a second magneticlayer was formed with an incident angle range of 70° to 50°. Cobalt wasloaded on evaporation source 120 and melted using a 60 kW electron beam.Oxygen was introduced from oxygen supply nozzle 170 at a rate of 1.0liter per minute. A film with a thickness of 0.06 μm was formed byadjusting the running speed of substrate 100.

The sample thus prepared was slit into a tape, and its read/writecharacteristics were examined. The read/write characteristics weremeasured using a ring-type magnetic head composed of Sendust and with a0.15 μm gap length. Playback output was determined as a value producedat a recording wavelength of 0.4 μm. The noise was determined as a noisewhich is 1 MHz lower than the frequency of the recording signal when asignal with a recording wavelength of 0.4 μm is recorded. The resultsare shown in FIG. 9.

FIG. 9 shows the dependency of the playback output and the noise on thethickness of the first magnetic layer. As the thickness of the firstmagnetic layer increases, the playback output increases and reaches thesaturation point. This phenomenon appears to be attributable to anincrease in the functionality of the first magnetic layer as an underlayer with an increase in film thickness. At a film thickness of 0.01 μmor greater, it appears that the functionality becomes sufficientlypronounced to be detectable. The noise also increases with an increasein the thickness of the first magnetic layer. At a film thickness of0.06 μm or greater, the noise increases rapidly, suggesting themanifestation of the influence of an increase in the granularity ofcolumnar particles. This trend remains the same even if the thickness ofthe second magnetic layer is changed. It should be noted, however, thatthe absolute value of noise increases with an increase in the thicknessof the second magnetic layer. FIG. 9 indicates the optimum range of filmthickness for the first magnetic layer.

(Embodiment 2)

A magnetic layer was formed by the same method as in Embodiment 1. Therunning speed of substrate 100 was adjusted in order to form a film witha 0.02 μm thickness as the first magnetic layer. A second magnetic layerwith a thickness of 0.02 μm to 0.2 μm was formed by varying the runningspeed of substrate 100. The sample, prepared in the same manner as inEmbodiment 1, was slit into a tape, and its read/write characteristicswere examined. The results are shown in FIG. 10.

FIG. 10 shows the dependency of the playback output and the noise on thethickness of the second magnetic layer. As the thickness of the secondmagnetic layer increases, the playback output increases and reaches thesaturation point. This indicates that a minimum total thickness of 0.5μm is required for the magnetic layers. The noise also increases with anincrease in the thickness of the second magnetic layer. At a filmthickness of 0.1 μm or greater, the noise increases rapidly, suggestingthe manifestation of the influence of an increase in the granularity ofcolumnar particles. This trend remains the same even if the thickness ofthe first magnetic layer is changed. It should be noted, however, thatthe absolute value of noise increases with an increase in thickness ofthe first magnetic layer, and the thickness of the second magnetic layerat which noise increases rapidly, shifts toward the smaller thicknessregion. The reason for this phenomenon may be that the grain-size of thecolumnar particles in the second magnetic layer inherits the grain sizeof the columnar particles in the first magnetic layer to some extent.Specifically, reducing the noise requires that the second magnetic layerbe slim to compensate for the thickness of the first magnetic layer, andif the first magnetic layer is slim, the noise level can be kept at aminimum even if the thickness of the second magnetic layer is increasedto some extent.

A systematic evaluation of the results of Embodiments 1 and 2 indicatesthat the most favorable conditions are a total film thickness range of0.05 μm to 0.12 μm for the magnetic layers, in which the thickness ofthe second magnetic layer is greater than or equal to 50% and less thanor equal to 80% of the total thickness. Further, from the standpoint ofplayback output and the C/N ratio, the desirable conditions are a totalfilm thickness range of 0.06 μm to 0.1 μm for the magnetic layers, inwhich the thickness of the second magnetic layer is greater than orequal to 60% and less than or equal to 75% of the total thickness.

(Embodiment 3)

A magnetic layer was formed by the same method as in Embodiment 1. Therunning speed of substrate 100 was adjusted in order to form a film witha 0.03 μm thickness as the first magnetic layer. A second magnetic layerwith a thickness of 0.07 μm was formed by adjusting the running speed ofsubstrate 100. The amount of oxygen introduced during the formation ofthe second magnetic layer was varied. The sample, prepared in the samemanner as in Embodiment 1, was slit into a tape and its read/writecharacteristics were examined. The results are shown in FIG. 11.

FIG. 11 shows the dependency of the playback output and the noise on theamount of oxygen introduced during the formation of the second magneticlayer. The figure indicates the existence of an optimum value of theamount of oxygen introduced relative to playback output. An oxygenamount greater than the optimum value precipitously reduces playbackoutput, apparently due to a significant decrease in the crystallinity ofcolumnar particles due to excess oxygen. Noise, on the other hand,decreases monotonically with an increase in the amount of oxygenintroduced. The reason for this phenomenon may lie in a decrease insaturation magnetization with an increase in the amount of oxygenintroduced and a promotion of the magnetic separation of columnarparticles. When the amount of oxygen introduced in FIG. 11 is from 0.6to 1.2 liters per minute, the easy axis direction of the sample is inthe range greater than or equal to 65° and less than or equal to 80°from the line normal to the film. On the other hand, the sample forwhich oxygen was introduced at a rate of 0.4 liter per minute exhibitsan easy axis direction of 93° from the line normal to the film.Similarly, the sample for which oxygen was introduced at a rate of 1.4liter per minute exhibits an easy axis direction of 58° from the linenormal to the film. This indicates the importance of controlling theeasy axis direction as a function of the amount of oxygen introduced. Inthis embodiment, the film deposition rate during the formation of thefirst magnetic layer was approximately one-third the film depositionrate during the formation of the second magnetic layer. Therefore, interms of the ratio of (amount of introduced oxygen)/(rate of filmdeposition), the value during the formation of the first magnetic layeris approximately 1.7 times the value that is observed when the secondmagnetic layer is formed by introducing oxygen at a rate of 1.6 litersper minute. This indicates the necessity for increasing the ratio of(amount of introduced oxygen)/(rate of film deposition) for theformation of the first magnetic layer. The ratio of (amount ofintroduced oxygen)/(rate of film deposition) is by no means fixed; itshould be adjusted appropriately so that the first magnetic layer isthicker than the second magnetic layer when these magnetic layers arecompared. Further, the results in FIG. 11 indicate that the range of theoptimum amount of oxygen introduced in order to obtain a high C/N ratiois narrow. This suggests the need for stringent control of the amount ofoxygen introduced.

In the next step, the Co--O film as a magnetic layer was formed usingthe magnetic recording medium fabrication equipment shown in FIG. 8. Apolyethylene terephthalate film 7 μm thick was used as substrate 100.The cylindrical drum used, reference numeral 200, had a 1.5 m diameter.

(Embodiment 4)

Shielding plates were installed so that the incident angle range for thefirst magnetic layer was from 85° to 75° and the incident angle rangefor the second magnetic layer was from 80° to 55°. Cobalt was loaded onevaporation sources 221 and 222. The amount of cobalt loaded onevaporation source 221 was one-third that loaded on evaporation source222. The power of the electron beam directed on the first evaporationsource was 20 kW and 60 kW for the second evaporation source. Oxygen wasintroduced at a rate of 0.4 liter per minute from oxygen supply nozzle271 and 1.0 liter per minute from oxygen supply nozzle 272. A film witha magnetic layer total thickness of 0.9 μm was formed by adjusting therunning speed of substrate 100.

The sample thus prepared was slit into a tape, its read/writecharacteristics were examined as in Embodiment 1 and compared with anoff-the-shelf ME tape. The results indicate that the tape fabricated inthis embodiment outperforms the off-the-shelf ME tape by greater than orequal to +7 dB in playback output and greater than or equal to +6 dB inC/N.

The tape produced in this embodiment exhibits excellent read/writecharacteristics apparently because of the high magnetic anisotropyenergy of the magnetic layer. Therefore, the magnetic anisotropy energylevels of the sample and the comparison tape were examined. The resultsindicate that whereas the off-the-shelf ME tape has an approximate K_(u)value of 1.4×10⁵ J/m³, the sample tape has an approximate K_(u) value of2.7×10⁵ J/m³. The tape of this embodiment appears to exhibit excellentperformance characteristics because of its high energy despite a smallfilm thickness.

(COMPARISON EXAMPLE 1)

A magnetic layer was formed using the same method as in Embodiment 4,except that the range of incident angle for the first magnetic layer wasfrom 90° to 75°. The sample thus prepared was slit into a tape and itsread/write characteristics were examined. However, the propensity of thetape surface to become scratched hampered the measurement process. Thecause of this problem appears to be the abnormal growth of crystalparticles due to the increase in the incident angle to 90°, which madethe abnormally grown crystal particles vulnerable to destruction whenthey slid against the head. The tape's anisotropy energy had a low K_(u)value of approximately 2.1×10⁵ J/m³.

(COMPARISON EXAMPLE 2)

A magnetic layer was formed using the same method as in Embodiment 4,except that the key-shaped component at the rear edge of shielding plate260 was removed in order to increase the spacing between the shieldingplate and cylindrical drum 200. The sample thus prepared was slit into atape and its read/write characteristics were examined. Both its playbackoutput and C/N were lower than the tape of Embodiment 4 by 3 to 4 dB.The tape's anisotropy energy had a low K_(u) value of approximately1.7×10⁵ J/m³, apparently because of the intrusion of the oxygenintroduced for the first magnetic layer into the initially formed sideof the second magnetic layer, resulting in a significant decrease in thecrystallinity of the second magnetic layer. This suggests the criticalimportance of adequate control over the amount of oxygen introduced. Astructure that permits a fast evacuation of excess oxygen is necessary.The results also suggest that oxygen should be introduced not at theinitial stage of film formation but toward the end of it.

Although the above embodiments used a 1.5 m diameter for cylindricaldrum 200, other diameter sizes are acceptable. Also, the amount ofoxygen introduced is by no means limited to the values used in theembodiments. Substrate 100 can be a film composed of a polymer materialother than polyethylene terephthalate. Conditions such as the positionsof evaporation sources, incident angle, and film thickness, can bevaried as long as they are in the ranges indicated in the presentinvention.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

What is claimed is:
 1. A magnetic recording medium fabrication devicefor forming a magnetic layer by vapor deposition on a substrate,comprising:a cooling drum for cooling the substrate at a low temperatureto control a growth of the magnetic layer while the substrate is runtherearound in a downstream direction; an evaporation source fordepositing the magnetic layer on the substrate; an ion gun forirradiating ions against the substrate, said ion gun being located justupstream from a plate-like shielding plate defining an initial angle ofdeposition of said evaporation source with respect to the substrate soas to remove impurities on the substrate prior to the deposition by saidevaporation source; and a cooling body for capturing gases struck outfrom the surface of the substrate by the irradiation of ions by said iongun, said cooling body being located between said ion gun and an area onthe substrate opposite to said ion gun and held at a temperature lowerthan the temperature of the substrate.
 2. The magnetic recording mediumfabrication device of claim 1, wherein a part of said cooling body is apipe and wherein a cooling medium flows in said pipe.
 3. The magneticrecording medium fabrication device of claim 1, further comprising ashielding plate arranged between said ion gun and said cooling body. 4.A magnetic recording medium fabrication device for forming magneticlayers on a substrate, comprising:a cylindrical drum for running thesubstrate therearound in a downstream direction, first and secondevaporation sources for depositing the magnetic layers on the substrate,said first evaporation source being positioned upstream said secondevaporation source, and both said first and second evaporation sourcesbeing positioned on a same side of a vertically extending plane passingthrough and including a rotational axis of said cylindrical drum; andshielding plates having first and second openings positioned betweensaid first and second evaporation sources, respectively, and saidcylindrical drum; wherein a horizontal distance between a center of saidfirst evaporation source and said vertically extending plane is greaterthan a radius of said cylindrical drum; wherein a horizontal distancebetween a center of said second evaporation source and said verticallyextending plane is less than the radius of said cylindrical drum; andwherein a vertical position of said first opening is higher than that ofsaid second opening.
 5. The magnetic recording medium fabrication deviceof claim 4, wherein said first and second evaporation sources arerespectively heated by first and second beams formed by splitting asingle beam from an electron beam source.
 6. The magnetic recordingmedium fabrication device of claim 4, wherein said first and secondevaporation sources are heated by electron beam irradiation, such thatan electron beam directed at either one of said first and secondevaporation sources does not intersect with evaporated atoms emittedfrom either other one of said first and second evaporation sources. 7.The magnetic recording medium fabrication device of claim 4, whereinsaid first evaporation source is smaller than said second evaporationsource.
 8. The magnetic recording medium fabrication device of claim 4,further comprising first and second oxygen supply nozzles forintroducing oxygen in an upstream direction and located in a vicinity ofsaid shielding plates downstream of said first and second openings,respectively.